1. Field of the Invention
The present invention relates to an optical data recording medium, for example, an optical disk and the like, and more specifically, to a recording medium an organic dye.
2. Prior Art
Recently, the development of an optical recording system mainly used for recording documents has been accelerated by the progress of an optical recording laser technology and a cost reduction thereof, the system recording and reproducing data by irradiating a laser beam on an optical disk.
The optical data recording mediums in this system includes a write once type optical data recording medium wherein a recording layer composed of a recording material containing an organic dye for a heat mode is formed on a substrate forming the optical data recording medium. This type of optical data recording medium is advantageous in that it can be made at a low cost because the recording layer can be formed by a coating method and that the recording density can be increased by making the intervals between pits narrower because a dye has a lower heat transfer rate than a method using a metal thin layer.
(Problems that the Invention is to Solve)
Conventionally, there is a proposal for this optical data recording medium which is provided with a recording layer composed of a material of chalcogens metal, metal oxide and the like These materials, however, are disadvantageous in that they are rare and the manufacturing cost thereof is expensive.
Further, there are proposals to use a material composed of various types of organic dyes having an infrared absorbing property such as a material in place of the above metals, an example of which is disclosed, for example, in Japanese Patent Kokai (Laid-Open) No. 61-243445 and characterized in that a recording layer is formed of a compound having the following. general formula: ##STR1## wherein, T may be equal to or different from T', in which each represents C, N, O or S, respectively.
A may be equal to or different from A', in which each represents an aromatic ring and further a substituent group --CH.sub.2 --nSO.sub.3.sup..crclbar. (n represents integer from 1 to 8) is attached to any one or both to form a salt with a nickel ion.
B may be equal to or different from B', in which each represents --H H-- (ring-open), --0--, --S--, ##STR2## (E represents a non-substituted or substituted alkyl group of C.sub.1 -C.sub.18 or non-substituted or substituted aromatic ring). ##STR3## --Se--, or --CH.dbd.CH--.
R and R.sup.(1) exist when T is C or N, R is equal to or different from R.sup.(1) and represent a non-substituted or substituted alkyl group of C.sub.1 -C.sub.18 or a non-substituted or substituted aromatic ring.
X.sup..crclbar. represents a halogen ion, peroxy halogenide ion, sulfonic acid ion, sulfate ion or acetate ion.
n represents an integer from 0 to 4, halogen, acetoxy, or benzoyloxy group may exist on a methyne chain at the center thereof or the methyne chain at the center may form a part of a ring.
This optical data recording medium, however, has a drawback in that it lacks sufficient durability to light and heat and sufficient resistance to reading light and further the recording layer composed of the above materials lacks sufficient enough writing sensitivity and C/N (carrier/noise) value and the like.
In addition, a conventional heat mode recording medium having a recording layer composed of polymethyne organic dye is added with anionized quencher as a stabilizer or provided with a protective layer composed of polymer a formed on a dye thin film experimentally to make the dye thin film unsusceptible to a change in a chemical structure caused by heat. The method of adding the anionized quencher as the stabilizer has a problem in that a light absorbing property and reflection factor which affect a recording property to be lowered since a dye ratio in a recording film is lowered by a decrease of the amount of dye by an increase of other substances entered therein. The method of forming the protective layer composed of the polymer has a problem in that enough pits are not formed since the protective film does not absorb light by itself and lack sufficient heat softening property. In conclusion, although both methods improve stability, both deteriorate a recording property which is very important to the recording medium, and thus these methods do not fundamentally solve the problems.
Note, that examples of the arrangement of the recording mediums previously proposed include a thin film composed of polystyrene or the like formed on a single dye recording film as a protective layer (Japanese Patent Kokai No. 58-36490), a resin layer formed on a cyanine film (Japanese Patent Kokai No. 59-203252) and the like.